Jeff,
That PSI number is just a reference to go by really.
I set my compressor at 15 PSI static pressure, and when the airbrush trigger is pressed it drops a pound or two. I always use static pressure (with the airbrush at rest) as what it says while spraying doesn't matter as long as it is enough pressure to make the paint atomize well and the paint job looks good.
“Wisdom is the right use of knowledge. To know is not
to be wise. Many men know a great deal, and are all the greater fools
for it. There is no fool so great a fool as a knowing fool. But to know
how to use knowledge is to have wisdom. " Charles Spurgeon